1. Field of the Invention
The invention relates to a record carrier carrying main information therein together with a series of subcode frames which each comprise a "copy" bit.
2. Description of the Related Art
Record carriers which carry digitized audio information have been available for a considerable time. Such a record carrier may be, for example, an optically readable disc, such as a "Compact Disc" or a magnetic tape, such as "DAT" cassette tapes. The advantage of digitized audio information is the extremely high quality of the recording. Another property of digitized information is that it can be copied to an almost unlimited extent without any significant loss of quality.
This last-mentioned property constitutes a substantial problem when consumer equipment in which digital audio information cannot only be reproduced from a record carrier but can also be re-recorded on another record carrier is marketed. This is because such equipment makes possible large scale copyright infringement by a customer thereof because the contents of a record carrier carrying copyrighted digitized audio information can easily be copied. Since there is no loss of quality as a result of copying, there is hardly any reason for the consumer to purchase a comparatively expensive original which is subject to copyright if the original or a copy thereof is available. All of this leads to a substantial loss of copyright revenues.
A recent copy protection method which mitigates the above drawbacks is known as the "Solocopy" copy-protection system. This method allows only first-generation copies to be made of record carriers carrying original information. In the "Solocopy" copy-protection system, it is assumed that the digital information to be recorded complies with a standard audio interface format, as described in, for example, the first edition (1989.03) of the IEC-958 standard. Such a format comprises main information channels and subcode information channels. The subcode information signal includes a "copy" bit indicating whether the information may be copied freely, and a category code indicating the source of the recorded information.
In accordance with the "Solocopy" copy protection method, it is ascertained by means of the category code and the "copy" bit whether the applied information may be copied. For example, copying is always allowed if the category code indicates that the information originates from a CD player. This is based on the assumption that a CD player is only capable of playing CDs of the read-only type. However, more recently, recording devices have been developed by means of which information can be recorded on a CD record carrier, which information can subsequently be read therefrom by a standard CD player for reading CDs of the read-only type.
Therefore, the prior-art "Solocopy" copy-protection method does not inhibit copying of CD information recorded on an inscribable optical record carrier. It is an object of the invention to provide means which mitigate this drawback.